Star Wars: The Last Jedi - 9 Moments Everybody Misunderstands
3. Rose Saving Finn
Of course, when the Resistance eventually makes it to Crait, it becomes apparent that Finn didn't quite take the right lesson from Canto Bight. With the First Order using a battering ram cannon to break through the shield gate, Finn takes matters into his own hands and, when the Resistance make their move, is ready to fly straight into the cannon. This would admittedly take it out, but also end his life, with the former Stormtrooper now thinking that there are things worth giving your life for.
And then Rose crashes into his ship and saves him. Which is, to the detractors, a move that robs Finn of his big heroic moment, potentially dooms the Resistance, and leaves the character with nowhere to go in Episode IX.
The final part is the easiest to understand, because it's not clear what part Finn will play in Episode IX. But then, it's not clear what part anyone will play in the ninth instalment, really - thanks to this movie, we're off-template for Star Wars films, there's not much more to "rhyme" with, and it can go in just about any direction it wants. Finn's still alive, he still has Rey to reconnect with, a romance with Rose on the cards, a huge fight against the First Order, and a backstory to explore. He'll be just fine in 9.
Finn flying into that cannon would've been a heroic moment but, as Leia said to Poe earlier in the film: "Dead heroes. No leaders." Sacrifice and hope are twin pillars of the franchise as two of its core themes, and they're right at the heart of this movie. Moving away from sacrifice is a lesson Poe learned the hard way, after the deaths of Holdo, Paige, and countless others. Finn gets to learn it here. Had he, the man considered a big deal in the Resistance, died in that instance, then it would've undercut the current of hope that runs through the galaxy afterwards. The message would've been about people dying for the cause, but living is much more hopeful.
It's true that, at this point, Rose doesn't know Luke is going to (sort of) turn up and save the day, but taking out the cannon wouldn't really have solved much. It would've bought the Resistance a bit more time, sure, but without Luke the First Order would've broken through eventually anyway, and had the pain of losing Finn too. "I saved you, dummy. That’s how we’re going to win. By saving the things we love, not destroying the things we hate.” It's corny, but then Star Wars has always been a bit corny (in a good way), and its message (and the act it follows) is far more hopeful and helpful to the ultimate cause of lighting the spark than Finn committing suicide.